Life on other planets could be far more widespread, study finds

Jan 07, 2014

Planets previously considered uninhabitable may be able to sustain life according to research from the University of Aberdeen

(Phys.org) —Earth-sized planets can support life at least ten times further away from stars than previously thought, according to academics at the University of Aberdeen.

A new paper published in Planetary and Space Science claims cold rocky planets previously considered uninhabitable may actually be able to support life beneath the surface.

The team, which included academics from the University of St Andrews, challenge the traditional 'habitable zone' – i.e. the area of space around a star, or sun, which can support life – by taking into consideration life living deep below the ground.

"The traditional habitable zone is also known as the Goldilocks zone," explains PhD student Sean McMahon. "A planet needs to be not too close to its sun but also not too far away for liquid water to persist, rather than boiling or freezing, on the surface.

"But that theory fails to take into account life that can exist beneath a planet's surface. As you get deeper below a planet's surface, the temperature increases, and once you get down to a temperature where liquid water can exist – life can exist there too."

The team created a computer model that estimates the temperature below the surface of a planet of a given size, at a given distance from its star.

"The deepest known life on Earth is 5.3 km below the surface, but there may well be life even 10 km deep in places on Earth that haven't yet been drilled.

"Using our computer model we discovered that the habitable zone for an Earth-like planet orbiting a sun-like star is about three times bigger if we include the top five kilometres below the planet surface.

"The model shows that liquid water, and as such life, could survive 5km below the Earth's surface even if the Earth was three times further away from the sun than it is just now.

"If we go deeper, and consider the top 10 km below the Earth's surface, then the habitable zone for an Earth-like planet is 14 times wider."

The current habitable zone for our solar system extends out as far as Mars, but this re-drawn habitable zone would see the zone extend out further than Jupiter and Saturn. The findings also suggest that many of the so-called "rogue" planets drifting around in complete darkness could actually be habitable.

"Rocky planets a few times larger than the Earth could support liquid water at about 5 km below the surface even in interstellar space (i.e. very far away from a star), even if they have no atmosphere because the larger the planet, the more heat they generate internally.

"It has been suggested that the planet Gliese 581 d, which is 20 light years away from Earth in the constellation Libra, may be too cold for liquid water at the surface. However, our model suggests that it is very likely to be able to support liquid water less than 2 km below the surface, assuming it is Earth-like."

The significance of the subsurface is further illustrated by another paper published by the same team which suggests there could be more life below the surface of the continents on Earth thanthere is below the seafloor.

McMahon hopes the studies will encourage other researchers to consider how life on other planets might be detected.

"The results suggest life may occur much more commonly deep within planets and moons than on their surfaces. This means it might be worth looking for signs of life outside conventional habitable zones. I hope people will study the ways in which life below the surface might reveal itself. Because it's not unimaginable that there might be signs at the surface that life exists deep below.

"The surfaces of rocky planets and moons that we know of are nothing like Earth. They're typically cold and barren with no atmosphere or a very thin or even corrosive atmosphere. Going below the surface protects you from a whole host of unpleasant conditions on the surface. So the subsurface habitable zone may turn out to be very important. Earth might even be unusual in having life on the surface."

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Yes it is also believed that the gravitational tidal forces however that are exerted on Europa may provide a heat source for the vast ocean of water under the thick ice where life as we know it may very well thrive.

I certainly wouldn't say it is impossible. There are basically infinite possibilities when it comes to the conditions available on one world or another out there. Just about anything you can realistically imagine is probably out there somewhere.

However, I would suggest that life forming below the surface of a rocky planet doesn't seem very likely to me. It just doesn't seem like there would be enough freely circulating water, whether it is liquid or not. Sure, there's probably an exception out there somewhere, but that wouldn't make it likely.

I say we should continue to explore the solar system and then base our theories on what we find. It seems a bit premature to assume very much at this point. We don't even really know for sure whether there is liquid water on Titan yet, for example.

This news is already known or we would not have been discussing the possibility of life on the moons of Jupiter and Saturn. I think the concern with the Goldilocks zones is all about advanced life - like lizards and mammals fish etc. Not likely to get anything like that 2 km under the ground.

The surface habitable zone is not "a theory", it is a model of likeliest inhabitation (and easy detection of biosigns). There are already other HZs established such as the tidal HZ of ice moons.

What these people suggest is a crustal HZ. It is a pity if they didn't establish proprietary rights for that instead of criticizing established models.

That said, their result is _very_ exciting. I also didn't know that life was seen 5 km down, which is a lithostatic pressure of ~ 150 MPa [ http://www.geolog...rofi.gif ], or 1500 atmospheres. Compare to ocean trenches with life down to 10 km or 1000 atmospheres.

Antiscience creationist trolling science (verkle, Sinister - from their track record here) is hilarious! It is also helpful, because it makes many deconverts from dumb and non-factual magic ideas, see Dawkins's Convert's Corner.

@GS: There is water _in_ Titan though, it has an ammonia salty water ocean (which is where its nitrogen/methane atmosphere derives from). Predicted from moon models and the shell independent rotation.

The problem with terrestrials is that they likely have too much water in deep oceans. (Unless having a carbon mass fraction > 0.3, in which case there is no free water.) Half our water is circulating in the relatively cold crust. Granted, it is then diluted by rocks =D, but it is still plenty in cracks and subduction vents.

The later is the same vents that are now believed to likely be our geochemical ancestors. Even a putative stagnant-lid Archean Earth had subduction 10 % of the time to fulfill Sd ratio constraints. So there is hope for early Mars life, say.

Antiscience creationist trolling science (verkle, Sinister - from their track record here) is hilarious! It is also helpful, because it makes many deconverts from dumb and non-factual magic ideas, see Dawkins's Convert's Corner.

I don't know about verkle, but I've never promoted creationism. Must have me confused with someone else.

@GS: There is water _in_ Titan though, it has an ammonia salty water ocean (which is where its nitrogen/methane atmosphere derives from). Predicted from moon models and the shell independent rotation

We think there is water inside Titan, based on the reflection of ELF waves, but I'll repeat what I said above. It may be premature to say there is liquid water under the surface there. We don't know how deep or at what temperature, so lacking both temperature and pressure, it is impossible to say what phase state that supposed water might be in. We don't even know if Titan has a hot core or not. Extremely cold water under high pressure, with unknown chemicals in solution, might form exotic phases that are not liquid water. I think it is more accurate to say that liquid water under the surface of Titan has not been ruled out, rather than saying that there is liquid water. But maybe I'm too cautious.

The findings also suggest that many of the so-called "rogue" planets drifting around in complete darkness could actually be habitable.

This seems a bit of a stretch. It is true that the deeper you go on Earth the warmer it becomes, but you must also remember there is constant heat input from the Sun, which warms the Crust, not just the atmosphere and oceans. If the Earth were in deep space, the internal heat would escape faster since there'd be none of this solar input.

Remember, the greater a temperature difference, the faster heat conducts through a barrier. Since the heat from the Sun re-warms not only the surface, but the crust down to a depth of hundreds of meters. Temps get cooler for the first hundred meters or more, then they start to warm again. Without sunlight, this "log jam" effect from warmer surface temps wouldn't exist, and internal heat would bleed out faster (see insulation formula).

It might sound trivial at first, but it's not just about the instantaneous solar irradiance, but the cumulative difference it would make over geologic or cosmic time if a planet was tens or hundreds or ten thousand times farther away from a star.

Compute the solar constant of the Earth and multiply by a million years, for example, and that's a lot of energy. It's like 5.48e30 Joules, which is starting to get close to the GBE of a planet. This is more than the nuclear energy of all the radiologic material of a planet. A million years is peanuts compared to the several billion years numbers astrophysicists and geologists throw around.

It might sound trivial at first, but it's not just about the instantaneous solar irradiance, but the cumulative difference it would make over geologic or cosmic time if a planet was tens or hundreds or ten thousand times farther away from a star.

Compute the solar constant of the Earth and multiply by a million years, for example, and that's a lot of energy. It's like 5.48e30 Joules, which is starting to get close to the GBE of a planet. This is more than the nuclear energy of all the radiologic material of a planet. A million years is peanuts compared to the several billion years numbers astrophysicists and geologists throw around.

@Returnerswhat are you actually trying to say? are you claiming a young earth because it (earth) is not hot enough?

This seems a bit of a stretch. It is true that the deeper you go on Earth the warmer it becomes, but you must also remember there is constant heat input from the Sun

Earth has significant internal heating from the tidal force of the moon. I think it might be feasible for a rogue planet to maintain a stable internal temperature withing the range of liquid water as long as it has a large enough moon or moons.

I'm still skeptical about how sustainable such an environment might be though. I just don't see how water could circulate enough through the rocks to allow sufficient nutrient transport. We may have found life deep inside the Earth's crust, but that doesn't mean it could have started there, or that it could sustain itself without an active surface water cycle.

Waste of money to make stupid guesses about something that doesn't matter in the first place. Who funds this shit? Lets develop the technology to reach out and touch planets outside our solar system first. Then study and research where to go after that. Say in 1k-2k years. What a waste of smart people time and money. But good for them, they got published.

Waste of money to make stupid guesses about something that doesn't matter in the first place.

I agree. A technology to detect subsurface live on exoplanets can not be developed ( or if developed in the future, it would be almost irrelevant as it would come much much later than simpler technologies to detect surface live ) so no resources should be wasted on this. Only live existing on the surface of exoplanets could be observed one day, although we would need telescopes that are too expensive to make with today technology. The "habitable zone" definition can be useful in scientific texts if it refers to something that could be tested, not otherwise.

Methane is everywhere in the Universe. Carbon is the basic building block of life. It is natural to suppose that life in some form or other is the rule rather than the exception, if one accepts the anthropic principle. According to my observations, my understanding of how life works suggests to me that the farther away from the sun we decide to colonize, the longer will be our lifespans. We have to make sacrifices for living in this paradise we call Earth.

I accept the Goldilocks zone principle, but only if one is looking for life just like ours on Earth type planets just like ours. That's logical. If one is looking for any kind of life at all, even archaea like methanogens, one probably need look no further than deep in Mars, but that does not preclude life on or in Uranus or Neptune, those blue and green planets that beg exploration and analysis. Why are they blue and green?

I might have actually agreed with you on this, if our knowledge of Earth was still mired in the mid-1950's when I was born. Discovery of our deep sea trench chemosynthetic communities (in, what, the 1970's?) was a game changer, surely you know that, even if you weren't alive to see it. It's entirely possible, and perhaps likely, that Earth has been covered entirely in ice with only subsurface life enduring such an ice age. .There's no doubt that such articles are supposition, but why you would believe that "such cold planets would not have seas to begin with" is baffling--we certainly don't know that for a fact, as drilling and/or seismologic missions on Europa, Ceres, Enceladus, Ganymede et.al. are still in the future. Maybe you believe in fortune telling, but I don't believe you can see the future, and that's when such determinations will be made. Your claims are as baseless as you paint the article as being.

Does that support "life as we know it"? We don't know, because we haven't found it. I think this article jumps to conclusions.

In order to find it we will need to mount a manned expedition to Europa (a long way off at current technology), or at least a probe that can sample the geysers that may have been observed in recent observations of Europa.

I am not sure that the article is jumping to conclusions when we have found some pretty extreme forms of life on this planet, where no one expected such life to be found. If it happened here it could well have happened elsewhere. Only time, money and further empirical research will reveal it in the case of our solar system.

In any case, the point of the article is clear that we need to expand our horizons as to what environments are and aren't conducive to some forms of life--both existing and possible.

My accidental photo of 10 daylight UFOs has provided a lost pattern to successfully link UFOs to each other as well as countless ancient artifacts winning front page coverage in every newspaper in San Diegohttp://www.youtub...zqFRYaVY

It is true that the deeper you go on Earth the warmer it becomes, but you must also remember there is constant heat input from the Sun, which warms the Crust, not just the atmosphere and oceans. If the Earth were in deep space, the internal heat would escape faster since there'd be none of this solar input.

Earth's internal heat is not solely from solar radiance. A major portion of it is from the conversion of gravitational energy to retained-heat when it coalesced into being eons ago. The other not insignificant portion is from radioactive elements' decay. Thus, a planet far from any star, or in interstellar space, may very well be warm enough deep underground. It is a natural RTG.

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